Thermokeratoplasty system with a power supply that can determine a wet or dry cornea

ABSTRACT

A power supply for a thermokeratoplasty system. The power supply can be connected to an electrode and a return element that are both coupled to a cornea. The power supply can perform a test routine to determine whether the cornea is too “wet” or too “dry”.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a thermokeratoplasty probe thatis placed into direct contact with the outer surface of the cornea.

[0003] 2. Prior Art

[0004] Techniques for correcting vision have included reshaping thecornea of the eye. For example, myopic conditions can be corrected bycutting a number of small incisions in the corneal membrane. Theincisions allow the corneal membrane to relax and increase the radius ofthe cornea. The incisions are typically created with either a laser or aprecision knife. The procedure for creating incisions to correct myopicdefects is commonly referred to as radial keratotomy and is well knownin the art.

[0005] Present radial keratotomy techniques generally make incisionsthat penetrate approximately 95% of the cornea. Penetrating the corneato such a depth increases the risk of puncturing the Descemets membraneand the endothelium layer, and creating permanent damage to the eye.Additionally, light entering the cornea at the incision sight isrefracted by the incision scar and produces a glaring effect in thevisual field. The glare effect of the scar produces impaired nightvision for the patient. It would be desirable to have a procedure forcorrecting myopia that does not require a 95% penetration of the cornea.

[0006] The techniques of radial keratotomy are only effective incorrecting myopia. Radial keratotomy cannot be used to correct an eyecondition such as hyperopia. Additionally, keratotomy has limited use inreducing or correcting an astigmatism. The cornea of a patient withhyperopia is relatively flat (large spherical radius). A flat corneacreates a lens system which does not correctly focus the viewed imageonto the retina of the eye. Hyperopia can be corrected by reshaping theeye to decrease the spherical radius of the cornea. It has been foundthat hyperopia can be corrected by heating and denaturing local regionsof the cornea. The denatured tissue contracts and changes the shape ofthe cornea and corrects the optical characteristics of the eye. Theprocedure of heating the corneal membrane to correct a patient's visionis commonly referred to as thermokeratoplasty.

[0007] U.S. Pat. No. 4,461,294 issued to Baron; U.S. Pat. No. 4,976,709issued to Sand and PCT Publication WO 90/12618, all disclosethermokeratoplasty techniques which utilize a laser to heat the cornea.The energy of the laser generates localized heat within the cornealstroma through photonic absorption. The heated areas of the stroma thenshrink to change the shape of the eye.

[0008] Although effective in reshaping the eye, the laser based systemsof the Baron, Sand and PCT references are relatively expensive toproduce, have a non-uniform thermal conduction profile, are not selflimiting, are susceptible to providing too much heat to the eye, mayinduce astigmatism and produce excessive adjacent tissue damage, andrequire long term stabilization of the eye. Expensive laser systemsincrease the cost of the procedure and are economically impractical togain widespread market acceptance and use. Additionally, laserthermokeratoplastic techniques non-uniformly shrink the stroma withoutshrinking the Bowmans layer. Shrinking the stroma without acorresponding shrinkage of the Bowmans layer, creates a mechanicalstrain in the cornea. The mechanical strain may produce an undesirablereshaping of the cornea and probable regression of the visual acuitycorrection as the corneal lesion heals. Laser techniques may alsoperforate Bowmans layer and leave a leucoma within the visual field ofthe eye.

[0009] U.S. Pat. Nos. 4,326,529 and 4,381,007 issued to Doss et al,disclose electrodes that are used to heat large areas of the cornea tocorrect for myopia. The electrode is located within a housing thatspaces the tip of the electrode from the surface of the eye. Anisotropic saline solution is irrigated through the electrode andaspirated through a channel formed between the outer surface of theelectrode and the inner surface of the sleeve. The saline solutionprovides an electrically conductive medium between the electrode and thecorneal membrane. The current from the electrode heats the outer layersof the cornea. Heating the outer eye tissue causes the cornea to shrinkinto a new radial shape. The saline solution also functions as a coolantwhich cools the outer epithelium layer.

[0010] The saline solution of the Doss device spreads the current of theelectrode over a relatively large area of the cornea. Consequently,thermokeratoplasty techniques using the Doss device are limited toreshaped corneas with relatively large and undesirable denatured areaswithin the visual axis of the eye. The electrode device of the Dosssystem is also relatively complex and cumbersome to use.

[0011] “A Technique for the Selective Heating of Corneal Stroma” Doss etal., Contact & Intraoccular Lens Medical Jrl., Vol. 6, No. 1, pp. 13-17,January-March, 1980, discusses a procedure wherein the circulatingsaline electrode (CSE) of the Doss patent was used to heat a pig cornea.The electrode provided 30 volts r.m.s. of power for 4 seconds. Theresults showed that the stroma was heated to 70° C. and the Bowman'smembrane was heated 45° C., a temperature below the 50-55° C. requiredto shrink the cornea without regression.

[0012] “The Need For Prompt Prospective Investigation” McDonnell,Refractive & Corneal Surgery, Vol. 5, January/February, 1989 discussesthe merits of corneal reshaping by thermokeratoplasty techniques. Thearticle discusses a procedure wherein a stromal collagen was heated byradio frequency waves to correct for a keratoconus condition. As thearticle reports, the patient had an initial profound flattening of theeye followed by significant regression within weeks of the procedure.

[0013] “Regression of Effect Following Radial Thermokeratoplasty inHumans” Feldman et al., Refractive and Corneal Surgery, Vol. 5,September/October, 1989, discusses another thermokeratoplasty techniquefor correcting hyperopia. Feldman inserted a probe into four differentlocations of the cornea. The probe was heated to 600° C. and wasinserted into the cornea for 0.3 seconds. Like the procedure discussedin the McDonnell article, the Feldman technique initially reducedhyperopia, but the patients had a significant regression within 9 monthsof the procedure. To date, there have been no published findings of athermokeratoplasty technique that will predictably reshape and correctthe vision of a cornea without a significant regression of the cornealcorrection.

[0014] It would therefore be desirable to provide a thermokeratoplastytechnique which can predictably reshape and correct the vision of an eyewithout a significant regression of the visual acuity correction.

[0015] It would be desirable to know the electrical contact between anelectrode and the cornea before conducting an electro-thermokeratoplastyprocedure. A cornea that is too dry may create a high electricalimpedance that produces a relatively large amount of localized heatingin the tissue. A cornea that is too wet may dissipate the current sothat the corneal tissue is not sufficiently denatured. It would bedesirable to provide a power supply and technique that can test thecondition of the eye to determine if there is an acceptable electricalpath.

BRIEF SUMMARY OF THE INVENTION

[0016] The present invention includes a power supply for athermokeratoplasty system. The power supply can be connected to anelectrode and a return element that are both coupled to a cornea. Thepower supply can perform a test routine to determine whether the corneais too “wet” or too “dry”.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a perspective view of a thermokeratoplasty electrodesystem of the present invention;

[0018]FIG. 1a is a graph showing a waveform that is provided to theprobe of the system;

[0019]FIG. 1b is a graph showing the amount of typical vision correctionregression over time;

[0020]FIG. 1c is a representation of a nominal thermal profile withinthe cornea produced by the electrode system of the present invention;

[0021]FIG. 2 is a top view of an electrode probe of the system;

[0022]FIG. 3 is a side view of the probe in FIG. 2;

[0023]FIG. 4 is an enlarged view of the probe tip;

[0024]FIG. 5 is a side view showing the probe being used to treat anarea of the corneal membrane;

[0025]FIG. 6 is a top view showing a pattern of denatured areas of thecornea;

[0026]FIG. 7 is a perspective view of an alternate embodiment of theprobe;

[0027]FIGS. 8a-b show a method for performing a procedure of the presentinvention;

[0028]FIG. 9 shows a pattern of incisions and denatured areas to correctfor a myopic condition;

[0029]FIG. 10 shows another pattern of incisions and denatured areas tocorrect for hyperopic conditions;

[0030]FIG. 11 shows a preferred embodiment of the present invention;

[0031]FIG. 11a is an enlarged view of the tip of FIG. 11;

[0032]FIG. 12 is a perspective view of a probe with the return electrodeas a lid speculum that maintains the eyelid in an open position;

[0033]FIG. 13 is a side view of an alternate probe tip embodiment;

[0034]FIG. 14 is a side view of an alternate probe tip embodiment;

[0035]FIG. 15 is a side view of an alternate probe tip embodiment;

[0036]FIG. 16 is a side view of an alternate probe tip embodiment;

[0037]FIG. 17 is a side view of an alternate probe tip embodiment;

[0038]FIG. 18 is a side view of an alternate probe embodiment;

[0039]FIG. 19 is a schematic of a circuit which limits the use of aprobe beyond a predetermined useful life;

[0040]FIG. 20 is a side view of an alternate probe tip design;

[0041]FIG. 21 is an enlarged cross-sectional view of the probe tip;

[0042]FIG. 22 is an enlarged view of the probe tip inserted into acornea;

[0043]FIG. 23 is a side view of an alternate embodiment of an electrode;

[0044]FIG. 24 is a side view of an alternate embodiment of an electrode;

[0045]FIG. 25 is a side view of an alternate embodiment of an electrode;

[0046]FIG. 26 is a schematic of an embodiment of a power supply;

[0047]FIG. 27 is a flowchart showing an operation of the power supply;

[0048]FIGS. 28a-j are end views of alternate embodiments of anelectrode;

[0049]FIG. 29 is a cross-sectional view of an alternate embodiment of aprobe assembly;

[0050]FIG. 30 is a cross-sectional view showing a probe holder for theprobe of the assembly shown in FIG. 29;

[0051]FIG. 31 is a cross-sectional view of an alternate embodiment of aprobe assembly;

[0052]FIG. 32 is an enlarged cross-sectional view of a probe of theassembly shown in FIG. 30;

[0053]FIG. 33 is a cross-sectional view of an alternate embodiment of aprobe assembly;

[0054]FIG. 34 is a side view showing an alternate embodiment of a handlefor a probe assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0055] Referring to the drawings more particularly by reference numbers,FIG. 1 shows a thermokeratoplastic electrode system 10 of the presentinvention. The system 10 includes an electrode probe 12 coupled to apower supply unit 14. The power supply unit 14 contains a power supplywhich can deliver power to the probe 12. The probe 12 has a hand piece16 and wires 18 that couple the probe electrodes to a connector 20 thatplugs into a mating receptacle 22 located on the front panel 24 of thepower unit. The hand piece 16 may be constructed from a non-conductivematerial and is approximately 0.5 inches in diameter and 5 inches long.

[0056] The power supply 14 provides a predetermined amount of energy,through a controlled application of power for a predetermined timeduration. The power supply 14 may have manual controls that allow theuser to select treatment parameters such as the power and time duration.The power supply 14 can also be constructed to provide an automatedoperation. The supply 14 may have monitors and feedback systems formeasuring tissue impedance, tissue temperature and other parameters, andadjust the output power of the supply to accomplish the desired results.The unit may also have a display that indicates the number of remaininguses available for the probe 12.

[0057] In the preferred embodiment, the power supply provides a constantcurrent source and voltage limiting to prevent arcing. To protect thepatient from overvoltage or overpower, the power unit 14 may have anupper voltage limit and/or upper power limit which terminates power tothe probe when the output voltage or power of the unit exceeds apredetermined value. The power unit 14 may also contain monitor andalarm circuits which monitor the resistance or impedance of the load andprovide an alarm when the resistance/impedance value exceeds and/orfalls below predefined limits. The alarm may provide either an audioand/or visual indication to the user that the resistance/impedance valuehas exceeded the outer predefined limits. Additionally, the unit maycontain a ground fault indicator, and/or a tissue temperature monitor.The front panel of the power unit typically contains meters and displaysthat provide an indication of the power, frequency, etc., of the powerdelivered to the probe.

[0058] The power unit 14 may deliver a power output in a frequency rangeof 5 KHz-50 MHz. In the preferred embodiment, power is provided to theprobe at a frequency in the range of 500 KHz. The unit 14 is designed sothat the power supplied to the probe 12 does not exceed 1.2 watts (W).The time duration of each application of power to a particular corneallocation is typically between 0.1-1.0 seconds. The unit 14 is preferablyset to deliver approximately 0.75 W of power for 0.75 seconds. FIG. 1ashows a typical voltage waveform that is applied by the unit 14. Eachpulse of energy delivered by the unit 14 is a highly damped signal,typically having a crest factor (peak voltage/RMS voltage) greater than10:1. Each power dissipation is provided at a repetitive rate. Therepetitive rate may range between 4-12 KHz and is preferably set at 8KHz.

[0059] The system has a switch which controls the application of powerto the probe 12. The power unit 14 also contains a timer circuit whichallows power to be supplied to the probe 12 for a precise predeterminedtime interval. The timer may be a Dose timer or other similarconventional circuitry which terminates power to the probe after apredetermined time interval. The unit may also allow the user to applypower until the switch is released. As one embodiment, the power supplymay be a unit sold by Birtcher Medical Co. under the trademarkHYFRECATOR PLUS, Model 7-797 which is modified to have voltage,waveform, time durations and power limits to comply with the above citedspecifications.

[0060] The power unit 14 may have a control member 26 to allow the userto select between a “uni-polar” or a “bi-polar” operation. The powersupply 14 may be constructed to provide a single range of numericalsettings, whereupon the appropriate output power, time duration andrepetition rate are determined by the hardware and software of the unit.The front panel of the power unit may also have control members (notshown) that allow the surgeon to vary the power, frequency, timerinterval, etc. of the unit. The return electrode (not shown) for auni-polar probe may be coupled to the power unit through a connectorlocated on the unit. The return electrode is preferably a cylindricalbar that is held by the patient, or an eye fixation electrode.

[0061] It has been found that at higher diopters, effective results canbe obtained by providing two different applications at the samelocation. Listed below in Table I are the power settings (peak power)and time duration settings for different diopter corrections (−d),wherein the locations (Loc) are the number of denatured areas in thecornea and dots/Loc is the number of power applications per location.TABLE I −d DOTS/LOC LOC PWR (W) TIME (SEC) 1.5 1 8 0.66 .75 2.5 2 8 0.66.75 3.5 2 8 0.83 .75 4.5 2 16 0.66 .75 6.0 2 16 0.83 .75

[0062] Using the parameters listed in Table I, the procedure of thepresent invention was performed on 36 different patients suffering fromsome degree of hyperopia. A pattern of 8-16 denatured areas were createdin the non-vision area of the eye. Patients who needed higher dioptercorrections were treated with high applications of power. FIG. 1b showsthe amount of regression in the vision correction of the eye. The eyeswere initially overcorrected to compensate for the known regression inthe procedure. As shown in FIG. 1b, the regression became stabilizedafter approximately 60 days and completely stabilized after 180 days.The error in overcorrection was within +/−0.5 diopters.

[0063]FIG. 1c shows nominal thermal profiles produced by the applicationof power to the cornea. As known to those skilled in the art, the corneaincludes an epithelium layer, a Bowmans membrane, a stroma, a Descemetsmembrane and a endothelium layer. Without limiting the scope of thepatent, the applicant provides the following discussion on the possibleeffects of the present method on the cornea of the eye. When power isfirst applied to the cornea the current flows through the center of thetissue immediately adjacent to the probe tip. The application of powercauses an internal ohmic heating of the cornea and a dehydration of thetissue. The dehydration of the tissue rapidly increases the impedance ofthe local heated area, wherein the current flows in an outward mannerindicated by the arrows in FIG. 1c. The cycle of dehydration and outwardcurrent flow continues until the resistance from the tip to the outerrim of the corneal surface, and the full thermal profile, issignificantly high to prevent further current flow of a magnitude tofurther cause denaturing of the corneal tissue. The direct contact ofthe probe with the cornea along the specific power/time settings of thepower source creates a thermal profile that denatures both the Bowman'smembrane and the stroma. The denaturing of both the Bowman's membraneand the stroma in a circular pattern creates a linked belt typecontracted annular ring. This annular ring will create a steepening ofthe cornea and sharpen the focus of the images on the retina. To controland minimize the denatured area, the surface of the eye is kept dry byapplying either a dry swab to the cornea or blowing dry air or nitrogenacross the surface of the eye.

[0064] The design of the power source and the high electrical resistanceof the denatured area provides a self limit on the amount of penetrationand area of denaturing of the cornea. Once denatured, the corneaprovides a high impedance to any subsequent application of power so thata relatively low amount of current flows through the denatured area. Ithas been found that the present procedure has a self limited denaturedprofile of approximately no greater than 75% of the depth of the stroma.This prevents the surgeon from denaturing the eye down to the Descemetsmembrane and endothelium layer of the cornea.

[0065]FIG. 1c shows nominal thermal profiles for diopter corrections of−1.5 d, −2.5-3.5 d and −4.0-6.0 d, respectively. In accordance withTable I, a −1.5 diopter correction creates a denatured diameter ofapproximately 1 mm and a stroma penetration of approximately 30%. A−2.5-3.5 d correction creates a denatured diameter of approximately 1.13mm and a stroma penetration of approximately 50%. A −4.0-6.0 dcorrection creates a denature diameter of approximately 1.25 mm and astroma penetration of approximately 75%.

[0066] FIGS. 2-5 show an embodiment of the probe 12. The probe 12 has afirst electrode 30 and a second electrode 32. Although two electrodesare described and shown, it is to be understood that the probe may haveeither both electrodes (bipolar) or just the first electrode (unipolar).If a unipolar probe is used, a return electrode (indifferent electrode)is typically attached to, or held by, the patient to provide a “return”path for the current of the electrode.

[0067] Both electrodes 30 and 32 extend from the hand piece 16 whichcontains a pair of internal insulated conductors 34 that are contactwith the proximal end of the electrodes. The first electrode 30 has atip 36 which extends from a first spring member 38 that is cantileveredfrom the hand piece 16. The electrode 30 is preferably constructed froma phosphor-bronze or stainless steel, wire or tube, that is 0.2-1.5 mmin diameter. The spring portion 38 of the first electrode 30 ispreferably 50 millimeters (mm) long. In one embodiment, the tip 36 hasan included angle of between 15-60°, 30° nominal, and a nose radius ofapproximately 50 microns. A majority of the electrode 30 is covered withan insulating material to prevent arcing, and to protect non-targettissue, the user and the patient. The relatively light spring force ofthe probe provides a sufficient electrode pressure without penetratingthe cornea.

[0068] The second electrode 32 includes a disk portion 40 which extendsfrom a second spring member 42 that is also cantilevered from the handpiece 16. The disk portion 40 is spaced a predetermined distance fromfirst electrode 30 and has an aperture 44 that is concentric with thetip 36. In the preferred embodiment, the disk portion 40 has an outerdiameter of 5.5 mm and an aperture diameter of 3.0 mm. The disk 40further has a concave bottom surface 46 that generally conforms to theshape of the cornea or sclera.

[0069] In one embodiment, the bottom surface 46 has a spherical radiusof approximately 12.75 mm and a griping surface to assist in thefixation of the eye. The second electrode 32 provides a return path forthe current from the first electrode 30. To insure proper grounding ofthe cornea, the surface area of the disk 40 is typically 20-500 timeslarger than the contact area of the tip 36. In the preferred embodiment,the second spring member 42 is constructed to have a spring constantthat is less than one-half the stiffness of the first spring member 38,so that the second electrode 32 will have a greater deflection per unitforce than the first electrode 30. As shown in FIG. 3, the tip 36 anddisk 40 are typically located at angles a′ and a″ which may rangebetween 30°-180°, with the preferred embodiment being 45°. As shown inFIG. 5, the probe 12 is pressed against the cornea to allow the secondelectrode 32 to deflect relative to the first electrode 30. The secondelectrode 32 is deflected until the tip 36 is in contact with thecornea.

[0070] For surgeons who prefer “two handed” procedures, the probe couldbe constructed as two pieces, one piece being the first electrode, andthe other piece being the second electrode which also stabilizes the eyeagainst corneal movement. Although the probe has been described andshown denaturing a cornea, it is to be understood that the probes andmethods of the present invention can be used to denature other tissuesto correct for wrinkles, incontinence, etc. For example, the probe couldbe used to shrink a sphincter to correct for incontinence. The techniquewould be basically the same with small closely spaced dots forming atightening line, belt or cylinder.

[0071]FIG. 6 shows a pattern of denatured areas 50 that have been foundto correct hyperopic conditions. A circle of 8 or 16 denatured areas 50are created about the center of the cornea, outside the visual axisportion 52 of the eye. The visual axis has a nominal diameter ofapproximately 5 millimeters. It has been found that 16 denatured areasprovide the most corneal shrinkage and less post-op astigmatism effectsfrom the procedure. The circle of denatured areas typically have adiameter between 6-8 mm, with a preferred diameter of approximately 7mm. If the first circle does not correct the eye deficiency, the samepattern may be repeated, or another pattern of 8 denatured areas may becreated within a circle having a diameter of approximately 6.0-6.5 mmeither in line or overlapping. It has been found that overcorrectedhyperopic conditions may be reversed up to 80% by applying a steroid,such as cortisone, to the denatured areas within 4 days of post-op andcontinued for 2 weeks after the procedure. The procedure of the presentinvention can then be repeated after a 30 day waiting period.

[0072] The exact diameter of the pattern may vary from patient topatient, it being understood that the denatured spots should preferablybe formed in the non-visionary portion 52 of the eye. Although acircular pattern is shown, it is to be understood that the denaturedareas may be located in any location and in any pattern. In addition tocorrecting for hyperopia, the present invention may be used to correctastigmatic conditions. For correcting astigmatic conditions, thedenatured areas are typically created at the end of the astigmatic flataxis. The present invention may also be used to correct radialkeratotomy procedures that have overcorrected for a myopic condition.

[0073] The probe and power settings have been found to create denaturedareas that do not reach the Descemets membrane. It has been found thatdenatured areas of the Bowmans layer in the field of vision may disturbthe patients field of vision, particularly at night. The presentinvention leaves a scar that is almost imperceptible by slit lampexamination 6 months after the procedure. It has been found that thedenatured areas generated by the present invention do not produce thestar effect caused by the refraction of light through the slits createdin a corrective procedure such as radial keratotomy.

[0074]FIG. 7 shows an alternate embodiment of a probe 60 which has aplurality of first electrodes 62 coupled to a cage 64. The cage 64includes a first ring 66 separated from a second ring 68 by a number ofspacers 70. The cage 64 can be connected to a handle (not shown) whichallows the surgeon to more easily utilize the probe 60.

[0075] The first electrodes 62 extend through apertures 72 in the rings66 and 68. The electrodes 62 can move relative to the cage 64 in thedirections indicated by the arrows. The probe 60 has a plurality springs74 located between the rings and seated on washers 76 mounted to theelectrodes 62. The springs 74 bias the electrodes 62 into the positionsshown in FIG. 7. In the preferred embodiment, the probe 60 includes 8electrodes arranged in a circular pattern having a 7.0 millimeterdiameter.

[0076] In operation, the probe 60 is pressed onto the cornea so that theelectrodes 62 move relative to the cage 64. The spring constant of thesprings 74 is relatively low so that there is a minimal counterforce onthe tissue. A current is supplied to the electrodes 62 through wires 78attached thereto. The probe 60 is preferably used as a uni-polar device,wherein the current flows through the tissue and into a return electrodeattached to or held by the patient. Alternatively, the probe 60 may bebi-polar wherein one or more of the electrodes 62 would provide powerand the other electrodes may provide a ground return path. The probe 60may be configured so that the diameter of the electrode placement isadjustable. The electrode placement can vary incrementally between 5.5,6.0, 6.5, 7.0, 7.5, 8.0, and 8.5 millimeters.

[0077]FIGS. 8a and 8 b show a preferred method of correcting forhyperopic conditions using the electrode system of the presentinvention. As shown in procedural block 100 refractive readings areinitially taken of both eyes with, and then without, cycloplasia. Inprocedure block 102, the interocular pressure and cornea thickness atthe center of the eye are taken with a tonometer and pacymeter,respectively. If the interocular pressure is 20 mm Hg or greater, forI.O.P. reduction, 1 drop of a 0.5% solution marketed under the trademark“Betagan” is applied to the cornea twice a day for 2-3 months and theninitial test are repeated. A topography reading of the eye is then takento determine the shape of the cornea in procedural block 104.

[0078] Approximately 30 minutes before the application of the electrode,the patient is given a mild tranquilizer such as 5 mg of valium, and thesurgeon administers drops, such as the drops marketed under thetrademark “Madryacil”, to dilate the pupil and freeze accommodation, inblock 106. Immediately before the procedure, 2 drops of a topicalcocaine commonly known as “Proparacaine” is administered to the eyes inblock 108. In block 110 an in line microscope light is directed to thecornea for marking purposes. Then the lighting may be directed in alateral direction across the cornea. Laterally lighting the eye has beenfound to provide good visualization without irritating or photobleachingthe retina.

[0079] In procedural block 112, the surgeon marks 8 or 16 spots on thecornea, wherein the pattern has a preferred diameter of approximately 7mm. The surgeon sets the power and duration setting of the power unit tothe proper setting. In block 114, the surgeon then places the tip at oneof the spot markings and depresses the foot switch of the system, sothat power is supplied to the probe and transferred into the cornea.This process is repeated at all of the spot markings. The epithelium ofthe denatured areas are then removed with a spatula in block 116. If adiopter correction of −2.5-3.5 d, or −4.0-6.0 d is required the tip isagain placed in contact with the spots and power is applied to thecornea to generate a deeper thermal profile in the stroma. The procedureis then checked with an autorefractor.

[0080] The eyes are covered with a patch or dark glasses, and thepatient is given medication, in block 118. The patient preferably takesan antibiotic such as a drug marketed under the trademark “Tobrex” every2 hours for 48 hours, and then 3 times a day for 5 days. The patientalso preferably takes an oral analgesic, such as a drug marketed underthe trademark “Dolac”, 10 mg every 8 hours for 48 hours and a drugmarketed under the trademark “Globaset” every 8 hours for 48 hours. Ifthe patient has been overcorrected, the procedure can be reversed bywaiting 3-4 days after the procedure and then administering to the eyes1 drop of a steroid such as cortisone, 3 times a day for 1-2 weeks.

[0081]FIG. 9 shows a pattern of denatured areas 130 combined with apattern of incisions 132 that can correct myopic conditions. Theincisions can be made with a knife or laser in accordance withconventional radial keratotomy procedures. The incisions are made from a3.5 mm diameter to within 1 mm of the limbus at a depth of approximately85% of the cornea. Denatured areas are then created between theincisions 132 using the procedure described above. The power unit ispreferably set at 0.75 W of power and a time duration of 0.75 seconds.The slow heating of the cornea is important for minimizing regression,and as such 0.75 seconds has been found to be a preferable time durationto account for the patients fixation ability and the surgeons reactiontime. The denatured areas pull the incisions to assist in the reshapingof the cornea. This procedure has been found to be effective for dioptercorrections up to +10.0 d. Penetrating the cornea only 85% instead ofconventional keratotomy incisions of 95% reduces the risk of puncturingthe Descemets membrane and the endothelium layer. This is to bedistinguished from conventional radial keratotomy procedures whichcannot typically correct for more than 3.5 diopters.

[0082] The denatured pattern shown in FIG. 6 has been shown to correctup to 7.0 diopters. As shown in FIG. 10, a circumferential pattern ofincisions 134 may be created in addition to a pattern of denatured areas136, to increase the correction up to 10.0 diopters. The incisions willweaken the eye and allow a more pronounced reshaping of the eye. Thepattern of incisions may be created at either a 6 mm diameter or a 8 mmdiameter. The incisions typically penetrate no greater than 75% of thecornea. The contractive forces of the denatured areas may create gaps inthe incisions. It may be preferable to fill the gaps with collagen orother suitable material.

[0083]FIG. 11 shows an alternate embodiment of a probe which has asingle electrode 140. The electrode 140 has a tip 142 which ispreferably 0.009 inches in diameter. The tip extends from a spring beam144 that is bent so that the surgeon can place the tip onto the corneaover nose and brow without impairing the surgeon's vision. The springbeam 144 is preferably insulated and is 0.2-1.5 mm in diameter. Thespring beam 144 extends from a base 146 that is inserted into the handpiece. The base 146 is preferably constructed from stainless steel andis 0.030-0.125 inches in diameter, with a preferred diameter of0.060-0.095 inches.

[0084] As shown in FIG. 11a, the end of the tip 142 is preferably flatand has a textured surface 148. The textured surface 148 slightly gripsthe cornea so that the tip does not move away from the marking whenpower is applied to the eye.

[0085] As shown in FIG. 12, the probe 200 has a return electrode lidspeculum 202 that maintains the eye lid in an open position. Thespeculum 202 has a pair of cups 204 located at the end of wire 206. Thecups 204 are placed under an eye lid and maintain the position of thelid during the procedure. Extending from the lid speculum 202 is a wire208 that is typically plugged into the unit 14 “return” connector. Ithas been found that the procedure of the present invention will producemore consistent results when the probe 200 uses the lid speculum 202 asthe return electrode. The impedance path between the probe 200 and thelid speculum 202 is relatively consistent because of the relativelyshort distance between the lid speculum 202 and the probe 200, and thewet interface between the cornea and the lid speculum 202.

[0086] FIGS. 13-15 show alternate probe tip embodiments. The tips havesteps that increase the current density at the corneal interface. Thetips are preferably constructed from a stainless steel that is formed tothe shapes shown. The tip 220 shown in FIG. 13 has a cylindrical step222 that extends from a base 224. The step 222 terminates to a point,although it is to be understood that the end of the step 222 may have aflat surface. In the preferred embodiment, the base 224 has a diameterof 350 microns (um), and the step 222 has a diameter of 190 microns anda length of 210 microns.

[0087] The tip 230 shown in FIG. 14, has a first step 232 extending froma base portion 234 and a second step 236 extending from the first step232. The end of the second step 236 may be textured to improve thecontact between the probe and the cornea. In the preferred embodiment,the first step 232 has a diameter of 263 microns and a length of 425microns, the second step 236 has a diameter of 160 microns and a lengthof 150 microns. The tip 240 shown in FIG. 15, has a first step 242 thatextends from a base portion 244 and a second tapered step 246 thatextends from the first step 242. In the preferred embodiment, the firststep 242 has a diameter of 290 microns and a length of 950 microns. Thesecond step 246 has a diameter of 150 microns, a length of 94 micronsand a radius of 70 microns.

[0088]FIGS. 16 and 17 show alternate probe tip embodiments which have anouter electrode concentric with an inner electrode. The electrodes arecoupled to the unit so that the electrodes can provide current to thecornea either simultaneously or sequentially. By way of example, it maybe desirable to initially apply power to the cornea with the innerelectrode and then apply power with the outer electrode, or apply powerwith both electrodes and then apply power with only the outer electrode.Assuming the same current value, the inner electrode will apply powerwith a greater current density that the outer electrode. The dualelectrode probes allow the surgeon to create different thermal profiles,by varying the current densities, waveforms, etc. of the electrodes.

[0089] The probe 250 shown in FIG. 16 has an inner electrode 252 that isconcentric with an intermediate layer of insulative material 254 and anouter conductive layer 256. In the preferred embodiment, the innerelectrode 252 may have a diameter of 125 microns and extend from theouter layers a length of 150 microns. The outer layer 256 may havediameter of 350 microns. The inner electrode 252 may be capable of beingretracted into the insulative layer 254 so that the inner electrode 252is flush with the outer electrode 256, or may be adjusted between flushand full extension, either manually or under servo control.

[0090]FIG. 17 shows another alternate embodiment, wherein the probe 260has an additional outer sleeve 262. The sleeve 262 has an internalpassage 264 that supplies a fluid. The fluid may be a gas thatstabilizes the current path to the cornea or a relatively high impedancesolution (such as distilled water) which provides a coolant for the eye.

[0091]FIG. 18 shows an economical detachable probe 270 embodiment. Theprobe tip 270 has a conductive wire 272 that is located within a plasticouter housing 274. The probe tip 270 has a flexible section 276 thatextends from a body 278, preferably at a 45° angle. The tip 280 extendsfrom the flexible section 276, preferably at a 90° angle. Extending fromthe opposite end of the handle 278 is a male connector 282. Theconnector 282 may have a conductive sleeve 284 that is inserted into thesocket 286 of a female probe connector 288. The end of the wire 272 maybe pressed between the inner surface of the sleeve 284 and the outersurface of the male connector 282 to provide an electrical interconnectbetween the tip end 280 and the female probe connector 288. The sleeve284 may have a detent 290 to secure the probe tip 270 to the probeconnector 288. The probe tip end 280 may have distal shapeconfigurations similar to the tips shown in FIGS. 11, 13, 14, 15, 16, or17.

[0092]FIG. 19 shows a circuit 300 that will prevent the use of the probetip beyond a predetermined useful life. The circuit 300 has a pluralityof fuses 302 that are blown each time the probe is used for a procedure.The probe is rendered inoperative when all of the fuses 302 are blown.The circuit 200 typically has 10-30 fuses 302, so that the probe canonly be used 10-30 times. The circuit 300 (not shown) is preferablylocated on a printed circuit board (not shown) mounted to the probe. Thefuses 302 may be covered with a flash inhibitor such as silica sand toprevent fuse alloy splatter/spray when the fuses are blown.

[0093] In the preferred embodiment, the fuses 302 are connected todrivers 304 that are coupled to a plurality of serial to parallel shiftregisters 306. The clock pin (CLK) pins and input pin D of the firstshift register are connected to the unit 14. The unit 14 initiallyprovides an input to the first shift register and then shifts the inputthrough the registers 306 by providing a series of pulses on the clockpin CLK. An active output of a register 306 will enable thecorresponding driver 304 and select the corresponding fuse 302. The unit14 may clock the input through the shift registers 306 in accordancewith an algorithm contained in hardware or software of the unit, whereineach clock signal corresponds to the end of a procedure. By way ofexample, a clock signal may be generated, and a fuse blown, upon theoccurrence of four shots that have a power greater than 0.16 W and aduration greater than 0.25 seconds.

[0094] The circuit 300 may have a separate sample unit 308 that iscoupled to the unit 14 and the fuses 302. The sample unit 308 may havean optical coupler 310 which isolates the unit 14 from power surges,etc. or may be any voltage or current threshold/comparator circuitryknown in the art. The sample unit 308 may have a relay 312 that closes aswitch when the fuses 302 are to be sampled. The sample circuit 308samples the fuses 302 to determine how many fuses 302 are not blown. Thenumber of remaining fuses 302, which correlate to the amount ofprocedures that can be performed with that particular probe, may beprovided by a display on the unit 14. By way of example, after samplingthe fuses, the unit 14 may display the number 6 providing an indicationthat 6 more procedures can be performed with the probe. A 0 on thedisplay may provide an indication that the probe must be replaced.

[0095] To sample the fuses 302, the unit 14 sets relay 312 to “sample”and clocks an input through the registers 306. If the fuse 302 is notblown when the corresponding driver 304 is enabled by the output of theregister, the optical coupler 310 will be enabled. If the fuse 302 isblown the optical coupler 310 will not be enabled. The process ofenabling a driver 304 and monitoring the output of optical coupler 310is repeated for each fuse 302. The unit 14 counts the number of viablefuse links remaining to determine the remaining useful lives of theprobe.

[0096]FIG. 20 shows an alternate probe tip design 350. The probe tip 350includes a spring beam 352 that extends from a handle 354. Alsoextending from the handle 354 is a male connector 356. The maleconnector 356 can be connected to the female connector of the probeshown in FIG. 18. The connector 356 allows the tip 350 to be replacedwith a new unit. The handle 354 preferably has an outer plastic shell358 that can be grasped by the surgeon. The shell 358 is constructedfrom a dielectric material that insulates the surgeon from the currentflowing through the probe. The spring beam 352 is also typically coveredwith an electrically insulating material. Attached to the spring beam352 is a tip support member 360.

[0097] As shown in FIG. 21, the tip support 360 has a tip 362 whichextends from a stop 364. The tip 362 may be the point of a wire 366 thatextends to the spring beam 352. The wire 366 may be strengthened by athickened base portion 368. The thicker wire portion 368 can be either astepped single wire or a wire inserted into a hollow tube. There may bemultiple tip supports and tips 362 attached to a single spring beam 352.

[0098] As shown in FIG. 22, during a procedure, the tip 362 is insertedinto the cornea. The length of the tip 362 is typically. 300-600microns, preferably 400 microns, so that the electrode enters thestroma. The stop 364 limits the penetration of the tip 362. The diameterof the tip 362 is preferably 125 microns. The tip diameter is small tominimize the invasion of the eye.

[0099] The power supply provides a current to the cornea through the tip362. The current denatures the stroma to correct the shape of thecornea. Because the tip 362 is inserted into the stroma it has beenfound that a power no greater than 0.2 watts for a time duration nogreater than 1.0 seconds will adequately denature the corneal tissue toprovide optical correction of the eye. The frequency of the power istypically between 1-20 KHz and preferably 4 KHz. Inserting the tip 362into the cornea provides improved repeatability over probes placed intocontact with the surface of the cornea, by reducing the variances in theelectrical characteristics of the epithelium and the outer surface ofthe cornea.

[0100] In the preferred embodiment, the spring beam 352 is 0.90 incheslong with a diameter of 0.05 inches. The tip support may be 0.25 incheslong. The tip 362 may have an embedded layer of dielectric material 370that prevents current from flowing through the epithelium. The tip 362may be constructed from a 302 stainless steel wire that is subjected toa centerless grinding process. The grounded wire can then be exposed toa chemical milling process to create a sharp point.

[0101]FIG. 23 shows an alternate embodiment of a tip 370 wherein thespring beam 372 has a plurality of notches 374 to decrease the stiffnessof the beam 372. FIG. 24 shows an alternate embodiment of an electrode380 that has a coil spring 382 located between a tip 384 and a proximalend 386. Like the spring beams 352 and 372 the coil spring 382 allowsthe tip 384 to be displaced when the surgeon presses the electrode intothe cornea to prevent over-insertion of the tip 384. FIG. 25 showsanother embodiment of an electrode 390 with a folded flat spring 392located between a tip 394 and a proximal end 396.

[0102]FIG. 26 shows an embodiment of a power supply 400 that can providepower and determine the state of electrical contact between an electrode402, a cornea 404 and a return element 406. The electrode 402 may beconnected to an electrode pin 408 of the power supply 400. The returnelement 406 may be connected to a return pin 410 of the power supply400.

[0103] The electrode pin 408 and the return pin 410 may be connected toa current to voltage converter 412. The converter 412 provides an analogoutput voltage to an analog to digital A/D converter 414. The analogoutput voltage of the voltage converter 412 is a function of a voltagedrop between the electrode pin 408 and the return pin 410. The outputvoltage is also provided to a pulse counter 416.

[0104] The A/D converter 414 and pulse counter 416 may be connected to acontroller 418. The A/D converter 414 may provide the controller 418with a binary bit string that represents a value of the voltage from theconverter 412. The A/D converter 414 may include a sample and holdcircuit so that the converter 414 output corresponds to the peak voltageprovided by the converter 412. The pulse counter 416 may provide afeedback signal to the controller 418 to provide an indication thatenergy was delivered to the cornea 404.

[0105] The controller 418 may be connected to a radio frequency (RF)pulse generator 420 and an output switch 422. The pulse generator 420may be an L-C circuit that produces a damped RF waveform in response toan impulse from the controller 418. The controller 418 may generate aseries of impulses that produce a series of damped waveforms that areprovided to the cornea 404. By way of example, each impulse may be afive volt, one nanosecond pulse provided to the pulse generator 420. Thecontroller 418 may perform an automatic gain control function toincrease or decrease the amplitude of the impulse provided to the pulsegenerator 420 as a function of the feedback signal. For example, thecontroller 418 may decrease the amplitude for a dry cornea and increasethe amplitude for a wet cornea.

[0106] The output switch 422 may be switched between an on state and anoff state. In the off state the output provides a safety feature,wherein power is not supplied to the cornea 404.

[0107] The controller 418 may be connected to a DC power supply 424 anda display 426. The display 426 may include a pair of indicator lightsdesignated “wet” and “dry”. The controller 412 may also be connected toa power adjustment circuit 428, a time adjustment circuit 430 and aswitch 432. The switch 432 may be a footswitch or a handswitch that canbe manipulated by the surgeon to initiate a routine of the controller418. The adjustment circuits 428 and 430 allow the surgeon to vary thelevel and time duration of energy provided to the electrode 402,respectively.

[0108] The controller 418 may perform a software routine in accordancewith an algorithm shown in FIG. 27. Initially, the surgeon couples thereturn element 404 to the cornea and places the electrode 402 in contactwith the cornea tissue. In step 500 the surgeon closes the switch 432which provides an input to the controller 418. The controller 418 willthen enter a test routine. In the test routine the controller 418provides a series of impulses to the pulse generator 420 to generate aseries of RF pulses in step 502. The controller 412 also switches theswitch 422 to an “on” state so that the pulses are transmitted to thecornea 404 through the electrode 402.

[0109] The amount of pulses provided during the test routine istypically a fraction of the pulses provided during normal operation. Forexample, if the power supply normally provides 4800 pulses per 0.6seconds to denature the cornea, the supply 400 may provide 100 pulsesduring the test routine. The lower amount of total energy allows thepower supply to test the electrical contact without providing enoughenergy to significantly effect the cornea.

[0110] The RF pulses return to the voltage converter 412 through thereturn element 406 and return pin 410. A value that is a function of thevoltage at the return pin 410 is provided to the controller 418 throughthe voltage 412 and A/D 414 converters in step 504.

[0111] The controller 418 may differentiate the voltage value providedby the A/D converter 414 to obtain the time rate of change of thevoltage and corresponding resistance in step 506. The differentiatedvoltage may be used because the tissue will undergo a slight change inresistance in response to the energy provided by the power supply.Although a differentiated voltage is described, it is to be understoodthat the controller 418 can utilize some other voltage characteristicsuch as an undifferentiated voltage amplitude. The controller 418 maythen compare the actual differentiated voltage value with an upperthreshold.

[0112] If the differentiated voltage value is equal to or greater thanthe upper threshold the controller 420 may generate a dry indicatoroutput signal to activate the dry indicator. In step 510, the activateddry indicator provides an indication that the cornea is too dry. Thecontroller 418 can also switch the switch 422 to the off state.

[0113] If the actual value is below the upper value the controller 418can compare the actual value to a lower threshold in step 512. If theactual value is less than or equal to the lower threshold then thecontroller may generate a wet indicator output signal that activates thewet indicator and turn off the switch 422 in step 514. If the actualdifferentiated value is not less than the threshold range, the testroutine will terminate and the controller 418 may continue to allowpulses to be provided to the cornea in step 516. The pulses are providedfor a time period that will denature the cornea.

[0114] It may be desirable to prevent the tip from rotating relative tothe handle to prevent any tearing of the cornea. FIGS. 28a-j showalternate embodiments of a proximal end of an electrode 500 that has ananti-rotation feature. The electrode 500 can be inserted into an opening502 of a handle 504. FIG. 28a shows an opening 502 with a key 506 thatfits within a corresponding slot 508 of the electrode 500. The key 506and slot 508 configuration prevent rotation of the electrode 500relative to the handle 504. Alternatively, the electrode 500 may havethe key 506 and the handle 504 may have the slot 508. FIG. 28b showsanother key type configuration wherein the handle 504 and electrode 500have matching flat surfaces 510.

[0115]FIGS. 28c-h show a handle 504 with a circular opening 502 and anelectrode 500 which has a dissimilar proximal end shape. FIG. 28c showsa square shaped proximal end, FIG. 28d shows a triangular shape, FIG.28e depicts a ellipsoidal shape, and FIG. 28f shows a hexagonal shape.FIG. 28g shows an electrode proximal end that has a plurality of camsurfaces that prevent relative rotation between the electrode 500 andthe handle 504. FIG. 28h shows an electrode 500 that has a spline 512.

[0116]FIG. 28i shows an electrode 500 that has a pair of beams 514 thatcan be inserted into a pair of corresponding openings 516 in a handle504. Alternatively, the handle 504 may have beams 514 and the electrode500 may have the openings 516. FIG. 28j shows an embodiment wherein theproximal end of the electrode 500 and the opening of the handle 504 bothhave a rectangular shape.

[0117]FIG. 29 shows an alternate embodiment of a probe tip assembly 550.The probe tip assembly 550 includes an arm 552 that holds a probe 554.The probe 554 may include an electrode 556 that extends through a probebody 558. A proximal end 560 of probe tip assembly arm 552 may beconnected to a power supply (not shown). The proximal end of theelectrode 556 may be connected to an apparatus that can pull on theelectrode 556 until the tip is exposed a desired length. Then theelectrode 556 can be attached to the probe body by crimping, solderingor other means. A distal end 562 of the electrode 556 may have a tip endthat is adapted to be placed in contact with a cornea. The handle 558may be constructed from a metal material that is partially coated with adielectric material such as paralene that prevents an electrical path tothe top surface of the cornea. The probe body 558 can be crimped orotherwise electrically connected to the electrode 556.

[0118] The probe body 558 may include an outer groove 564 that isadapted to receive a detent ball 566. The ball 566 may be biased intothe groove 564 by a spring 568. The ball 566 may be located within asleeve portion 570 of the arm 552. The probe body 558 may extend throughan inner channel 572 of the sleeve 570.

[0119] The probe 554 can be replaced by pulling the probe body 558 outof the inner channel 572. The inner groove 564 may have a taperedsurface such that the detent ball 566 is pushed out of the groove 564when the handle 558 is pulled out of the sleeve 570. A new probe 554 canbe inserted into the channel 572. The probe body 558 may have a stop 574that limits the insertion depth of the probe 554.

[0120]FIG. 30 shows a probe holder 590 that provides a protectiveinsertion package for the probe 554 shown in FIG. 29. The holder 590 mayinclude a sleeve 598 that has an inner channel 594 adapted to receivethe probe 554. The sleeve 598 may be constructed from a plastic materialsuch ABS or polyurethane. The channel 594 may include ribs 596 that gripthe probe. The holder 590 may also have a knurled outer layer 598 thatallows the operator to more readily grasp the sleeve 592 and push theprobe into the arm sleeve shown in FIG. 29.

[0121]FIG. 31 shows an alternate embodiment of a probe assembly 600. Theassembly 600 includes a probe 602 that is connected to an arm 604. Theprobe 602 may include a female socket 606 that receives a male pin 608of the arm 604. The socket 606 may include a dimple portion 610 thatexerts a pressure to secure the probe 602 to the pin 608.

[0122]FIG. 32 shows an embodiment of the probe 602. The probe 602 mayinclude an electrode 612 that extends through an inner channel 614 of aplastic sleeve 616. The electrode 612 may be connected to a hollow metalrivet 618 that is coupled to the female socket 606 shown in FIG. 31. Theelectrode 612 can be secured to the sleeve 616 with an adhesive 620. Theadhesive 620 can be cured with ultraviolet light. A tip portion 622 ofthe electrode 612 may extend from the end of the sleeve 612.

[0123]FIG. 33 shows an alternate embodiment of the probe assembly 600′wherein an electrode 612′ is wrapped through holes 624 in the sleeve616′ to create a “thread” within the probe 602′. The electrode 612′ canbe routed through the holes 624 after the wire is secured to the sleeve612′ by an adhesive 620.

[0124] The pin 608′ may have a corresponding groove 626 that can receivethe threaded electrode 612′. This embodiment provides a probe that has adielectric outer sleeve 616′ with an internal contact thread thatprovides an electrical path between the electrode tip and the male pin608′. The dielectric outer sleeve 616′ provides a protective element forthe probe.

[0125]FIG. 34 shows an embodiment of a handle 630 for a probe 632. Thehandle 630 may be connected to an electrode 634. The handle 630 may beconstructed from a molded and/or machined plastic material and have atextured outer surface 636. The handle 630 may have a size and shapethat allows a surgeon to hold the probe 632 with three fingers.

[0126] While certain exemplary embodiments have been described and shownin the accompanying drawings, it is to be understood that suchembodiments are merely illustrative of and not restrictive on the broadinvention, and that this invention not be limited to the specificconstructions and arrangements shown and described, since various othermodifications may occur to those ordinarily skilled in the art.

What is claimed is:
 1. An electrical power supply for athermokeratoplasty tip that can provide an indication of an electricalcharacteristic of a cornea, comprising: an electrode pin; a return pin;and, a circuit that can provide a test current to said electrode pin andthe cornea, and an indication of the electrical characteristic of thecornea in response to the test current flowing through the cornea andsaid electrode and return pins.
 2. The power supply of claim 1, whereinthe electrical characteristic is a function of a voltage at said returnpin.
 3. The power supply of claim 2, wherein the electricalcharacteristic is a time rate of change of the voltage at said returnpin.
 4. The power supply of claim 1, wherein said circuit provides aseries of radio frequency test pulses to said electrode pin.
 5. Thepower supply of claim 3, wherein a number of radio test pulses is lessthan a number of radio frequency operating pulses.
 6. The power supplyof claim 1, wherein said circuit provides a wet indicator output signalif the electrical characteristic is equal to or less than a lowerthreshold value and provides a dry indicator output signal if theelectrical characteristic is equal to or greater than an upper thresholdvalue.
 7. The power supply of claim 1, wherein said circuit provides aseries of operating radio frequency pulses if the electricalcharacteristic is greater than the lower threshold and less than theupper threshold.
 8. The power supply of claim 1, wherein said circuitvaries an amplitude of said operating radio frequency pulses inaccordance with the electrical characteristic.
 9. A method for testingan electrical contact between a thermokeratoplasty electrode, a corneaand a return element, comprising: transmitting a test current throughthe electrode, the cornea and the return element; comparing anelectrical characteristic of the cornea to a threshold value; and,generating an indicator output signal if the electrical characteristicis equal to or is greater than an absolute value of the threshold value.10. The method of claim 9, providing a series of radio frequencyoperating pulses if the electrical characteristic is less than theabsolute value of the threshold value.
 11. The method of claim 10,varying an amplitude of the radio frequency operating pulses inaccordance with the electrical characteristic.
 12. The method of claim9, wherein the electrical characteristic is a time rate of change of avoltage of a return pin.
 13. The method of claim 9, wherein a wetindicator output signal is generated if the voltage characteristic isequal to or less than a lower threshold value, and a dry indicatoroutput signal is generated if the electrical characteristic is equal toor greater than a upper threshold value.
 14. An electrode that can beinserted into an opening of a handle, comprising: a beam that a proximalend and a distal end, said proximal end being adapted to be insertedinto the handle opening and having an anti-rotation feature thatinhibits rotation within the handle opening.
 15. The electrode of claim14, wherein said beam has a tip at said distal end.
 16. The electrode ofclaim 14, wherein said anti-rotation feature includes a key.
 17. Theelectrode of claim 14, wherein said anti-rotation feature includes aflat surface within a circular shaped proximal end.
 18. The electrode ofclaim 14, wherein said anti-rotation feature includes a square shapedproximal end.
 19. The electrode of claim 14, wherein said anti-rotationfeature includes a triangular shaped proximal end.
 20. The electrode ofclaim 14, wherein said anti-rotation feature includes an ellipsoidalshaped proximal end.
 21. The electrode of claim 14, wherein saidanti-rotation feature includes a cam shaped proximal end.
 22. Theelectrode of claim 14, wherein said anti-rotation feature includes aspline formed within said proximal end.
 23. The electrode of claim 14,wherein said anti-rotation feature includes a pair of beams locatedwithin said proximal end.
 24. The electrode of claim 14, wherein saidanti-rotation feature includes a rectangular shaped proximal end. 25.The electrode of claim 14, wherein said anti-rotation feature includes ahexagonal shaped proximal end.
 26. A probe assembly, comprising: asleeve that has an inner channel; and, an electrode that is threadedwithin said inner channel and has a tip which extends from said sleeve.27. The probe assembly of claim 26, wherein said sleeve is constructedfrom a dielectric material.
 28. The probe assembly of claim 26, furthercomprising an adhesive that attaches said electrode to said sleeve. 29.A probe assembly, comprising: an arm; and, a probe that is coupled tosaid arm, said probe having an electrode that extends from a probe body.30. The probe assembly of claim 29, wherein said probe body extendsthrough an inner channel of an arm sleeve.
 31. The probe assembly ofclaim 29, wherein said arm includes a detent ball that is pressed intoan outer groove of said probe body.
 32. The probe assembly of claim 29,wherein said probe body includes a stop that engages said arm sleeve.33. The probe assembly of claim 29, wherein said arm has a male pin thatis inserted into a female socket of said probe.
 34. The probe assemblyof claim 29, further comprising a probe holder that captures said probe.